The present invention relates to a heating apparatus for heating a substrate to be treated, and in particular to a heating apparatus suitable for heating a resist pattern before or after exposure in photolithography or the like, a method for evaluating a heating apparatus and a pattern forming method.
Conventionally, a photolithography has been used to form a circuit pattern on a semiconductor apparatus. In the photolithography, heating process (bake) is performed on a resist before or after exposure. Regarding heating a semiconductor wafer (substrate to be treated) before or after exposure, the amount of heat supplied to the semiconductor wafer form a heating plate during heating process has conventionally thought to be constant, and the heating amount has been determined by effecting heating for a constant time period.
In such a method for controlling the heating amount, however, there is a problem that, since a temperature profile during heating is different for each wafer, the heating amount is actually different for each wafer. Also, as the temperature of a wafer can not be measured when there is a temperature distribution in the surface of the wafer, the temperature distribution in the intra-wafer can not be made uniform.
For this reason, when such a resist is used that its pattern dimension changes largely according to the heating amount, variations in dimension have occur on the intra-wafer and the inter-wafer. Furthermore, in the temperature measuring which has been conventionally performed with infrared light, it is the existing situation that, since the infrared light is longer in wavelength than visual light or ultraviolet light, a sufficient accuracy can not be obtained when optical change is monitored using the infrared light.
Also, in order to control a dimension of a resist pattern of intra-wafer with a high accuracy, it is important to control the treating temperature of a semiconductor substrate during heating uniformly and accurately. Specifically, in a lithography step, a temperature uniformity for a bake process after exposure, called PEB (Post Exposure Bake), is regarded as important due to introduction of a chemically amplifying type resist.
In order to attain an intra-wafer uniformity with a high accuracy, it becomes important to measure the surface temperature of a substrate during heating process in its surface accurately to control a heating apparatus.
As one method for measuring the surface temperature of a substrate during heat treatment, such a method is given that a product where such a temperature sensor as thermocouple is embedded in the same substrate as a substrate to be subjected to heat treatment, for example. Process Probe 1840 type manufactured by SensArray COP. is heat-treated to be used for a temperature measurement. However, when the bake process is performed in a sealed space in order to take out wires connecting the sensor which has been embedded in the treated substrate and a measuring unit from the bake unit, since the wire injures the sealing condition, it is difficult to reproduce the conditions of the processing time at a time of temperature measurement as it is, thereby lacking measuring accuracy. Also, as conditions such as a position where the substrate is disposed or the like can not be reproduced at the time of temperature measurement, there is a problem that a reliability of the measured result is injured.
Furthermore, when a bake process is effected in a state where such volatile material as solvent is included, a processing container (chamber) is generally exhausted and/or purged by such inert gas as air or nitrogen to form wind flow in the chamber in order to prevent the volatile material from attaching to the processing chamber. When a temperature measurement is conducted by an apparatus where a sensor is embedded in a substrate, the wind flow is disturbed by the wire which has been drawn out, which means that a temperature measurement is performed in a state different from the actual processing state, thereby resulting in a factor deteriorating the measuring accuracy. Also, there is a problem that a temperature lowering due to the exhaust wind can not be measured accurately due to a sealing resin for fixing the sensor.
In order to solve this problem, there has been proposed in Jpn. Pat. Appln. KOKAI Publication No. 11-8180 a method where the surface temperature of a substrate during the bake process is measured over its entire region by an infrared sensor (an infrared thermography process) which has been assembled in a bake unit and temperature control of respective divided heaters is performed on the basis of the temperature distribution information obtained. However, there is a problem that a sufficient measuring accuracy can not be obtained since the value of the temperature measured using the infrared temperature sensor largely depends on a film structure of film thickness of a substrate. There is also a problem that, since an infrared temperature sensor with a high accuracy which can measure a substrate over its entire surface is very expensive in general, the cost for manufacturing the bake unit is increased so that the back unit is impractical.
Meanwhile, there has been proposed in Jpn. Pat. Appln. KOKAI Publication No. 10-275755 a method and an apparatus where the line width of a latent image (an exposed portion/an unexposed portion) after PEB is measured and the measured result is fed back to the PEB temperature condition. In this method, however, there is a merit that no expensive measuring equipment is mounted on the bake unit, but there has occurred a problem that, as the resist latent image does not be made rectangular, it is difficult to measure the line width of the latent image and it is also difficult to feed back the measured result to the PEB temperature condition with a high accuracy.
Also, it is generally difficult to expose an intra-wafer with the completely same exposing amount and variations among respective shots occur. For this reason, it is necessary to uniform the temperature distribution and simultaneously to uniform a distribution of exposing amount actually incident on a resist in order to suppress the variations in dimension. However, it has been impossible to measure the temperature distribution and the actual irradiated exposing amount accurately.
Thus, there has conventionally a problem that, when the heating process is performed before or after exposure on the substrate to be treated on which a resist has been applied, it is impossible to accurately measure the heating amount of the substrate to be treated, to that variations occur in dimension.
Also, the heating temperature of the substrate to be treated can accurately be measured during the heating process so that it is impossible to evaluate a heating apparatus. Also, as the heating temperature can accurately be measured, there is a problem that the heating apparatus can not be controlled so that evenness of the heating temperature occurs in the intra-substrate and variations occurs in dimension of the resist pattern.
Also, there is a problem that the temperature distribution and the distribution of exposing amount of light which has been irradiated actually can accurately not be measured so that an exposing apparatus and the heating apparatus can not be evaluated. Furthermore, there is a problem that since the actual exposing amount and heating temperature can not be measured accurately so that the exposing apparatus and the heating apparatus can not be controlled, thereby resulting in that variations occur in dimension of the resist pattern.
The present invention has been attained in view of the above circumstances and its object is to provide a heating apparatus which can control heating temperature of a substrate to be treated to be constant and which can contribute to reduction of variations in dimension of a resist pattern or the like.
Also, another object of the present invention is to provide a method for evaluating a heating apparatus where temperatures during heat treatment are accurately measured so that a temperature distribution can be obtained.
Furthermore, another object of the invention is to provide a method for evaluating a heating apparatus and an exposing apparatus where an exposing amount which has been irradiated during heat treatment and temperatures during the heat treatment are accurately measured so that an exposing amount distribution and a temperature distribution can be obtained.
Also, another object of the invention is to provide a pattern forming method which can reduce the variations in dimension of a resist pattern or the like by measuring temperatures during heat treatment to obtain a temperature distribution, thereby reducing the size irregularity of resist patterns.
Further, another object of the invention is to provide a pattern forming method which can reduce variations in dimension of a resist pattern or the like by accurately measuring the exposing amount which has been irradiated actually during exposure and temperatures during heat treatment to obtain performed by the heating means on the basis of the detected intensities of reflected lights.
Here, preferred embodiments of the present invention will be proposed as follows:
(1) The heating means has an electrical heating function and comprises a sample stand on which a substrate to be treated is placed.
(2) The visible light or the ultraviolet light irradiated on the substrate to be treated is light whose band has been narrowed.
(3) The light intensity detecting means irradiates light on any place on the substrate to be treated and detects film thickness change due to composition change in the resist on the substrate to be treated as change in the intensity of reflected light.
(4) The light intensity detecting means irradiates light on an exposure region on the substrate to be treated and detects a latent image change of a resist on the substrate to be treated, as change in the intensity of reflected light.
(5) The light intensity detecting means has a function capable of recognizing the detected region of the intensity of reflected light as an image and a function for calculating the intensity of the detected region.
(6) The light intensity detecting means includes a mechanism for moving a light detecting device to the detection region for detecting the intensity of reflected light, a optical system capable of detecting only the reflected light from the detection region, and a mechanism for calculating the intensity of the detection region.
(7) The heating controlling means determines the next heating amount on the basis of the accumulated heating amount obtained from the intensity of reflected light and controls the heating means so as to obtain the determined heating amount.
(8) The heating controlling means determines the next heating amount on the basis of differentiated value of the accumulated heating amount obtained the intensity of reflected light and controls the heating means so as to obtain the determined heating amount.
(9) The heating controlling means controls on/off of the heating means on the basis of the determined heating amount while the power of the heating means is kept constant.
(10) The heating controlling means controls current of the heating means on the basis of the determined heating amount while the voltage of the heating means is kept constant.
(11) The heating controlling means controls voltage of the heating means on the basis of the determined heating amount while current of the heating means is kept constant.
(12) The heating controlling means determines a time when the detected intensity of reflected light has become a predetermined intensity of reflected light at a heating terminating time obtained in advance as a heat treatment terminating time.
Also, according to a third aspect of the present invention, there is provided a method for evaluating a heating apparatus comprising: a step for forming a photosensitive resin film on a substrate; a step for performing exposure on a plurality of exposure regions on the photosensitive resin film in an irradiation amount Dopt; a step for performing heat treatment on the photosensitive resin film to measure the film thickness of the photosensitive resin film at an unexposed domain adjacent to each exposure region, thereby obtaining a film thickness difference xcex94Tr between the exposed domain and the unexposed domain; and a step for obtaining a heating temperature distribution from the film thickness difference xcex94Tr in each obtained exposure region and a relationship between a film thickness difference xcex94Tr which has been obtained in advance and heating treating temperature.
In this invention according to the third aspect of the present invention, it is preferable that the irradiation amount Dopt is set such that the change amount ∂xcex94Tr/∂T to the temperature of the film thickness xcex94Tr becomes an extreme value or the maximum value.
Also, according to a fourth aspect of the present invention, there is provided a method for evaluating a heating apparatus/an exposing apparatus, comprising: a step for forming a photosensitive resin film on a substrate; a step for applying irradiation amounts Dopt1 and Dopt2 different from each other to a first exposure portion and a second exposure portion adjacent to each other on a plurality of exposure regions on the photosensitive resin film by one time irradiation; a step for performing heat treatment on the photosensitive resin film to measure the film thickness of the photosensitive resin film at the first and second exposure portions on each exposure region and an unexposed domain adjacent thereto, thereby obtaining a film thickness difference xcex94Tr1 between the first exposure portion in each exposure region and the unexposed domain and a film thickness difference xcex94Tr2 between the second exposure portion and the unexposed domain; and a step for obtaining heating temperature during the heat treatment and a distribution of irradiation amount applied by one time irradiation from the film thickness differences xcex94Tr1 and xcex94Tr2 in each measured exposure region and a relationship between change in film thickness difference to change of exposing amount which has been obtained in advance and change in film thickness difference to change in treating temperature.
Also, the according to a fifth aspect of the present invention, there is provided a pattern forming method where pattern forming is performed, wherein after adjusting a heating apparatus including: a step for forming a photosensitive resin film on a substrate; a step for performing exposure on an exposure region on the photosensitive resin film in an irradiation amount Dopt; a step for performing heat treatment on the photosensitive resin film by a heating apparatus to measure the film thickness of the photosensitive resin film at an unexposed domain adjacent to the exposure region, thereby measuring a film thickness difference xcex94Tr between the exposure region and the unexposed domain; a step for obtaining heating temperature during the heat treatment from the film thickness difference xcex94Tr in the measured exposure region and a relationship between a film thickness difference xcex94Tr which has been obtained in advance and heating treating temperature; and a step for adjusting the heating apparatus from the obtained heating temperature, and the method comprising: a step for forming a resist film on a substrate to be treated; a step for transferring a pattern formed on a projection substrate onto the resist film; a step for performing heat treatment on the resist film by the heating apparatus; and a step for applying developing liquid to the resist film to selectively remove a portion of the resist film.
Furthermore, according to a sixth aspect of the present invention, there is provided a pattern forming method including a step for forming a resist film on a substrate to be treated; a step for performing exposure in an exposing amount Dopt to transfer a pattern formed on a projection substrate onto the resist film; and a step for applying developing liquid to the resist film to selectively remove a portion of the resist film, wherein, the heat treatment comprises the steps of; measuring the film thickness of the resist film at an unexposed domain adjacent to the exposure region to measure a film thickness difference xcex94Tr between the exposure region and the unexposed domain; obtaining heating temperature from the film thickness difference xcex94Tr in the measured exposure region and a relationship between a film thickness difference xcex94Tr which has been obtained in advance and heating treating temperature; and heating the resist film while the control conditions of the heating apparatus is being adjusted in response to the obtained the heating temperature.
In this invention according to the sixth aspect of the present invention, it is preferable that the irradiation amount Dopt is set such that the change amount a xcex94Tr/∂T to the temperature of the film thickness xcex94Tr becomes an extreme value or the maximum value.
Also, according to a seventh aspect of the present invention, there is provided a pattern forming method where after adjusting a heating apparatus/exposing apparatus including: a step for forming a photosensitive resin film on a substrate; a step for applying irradiation amounts Dopt1 and Dopt2 different from each other to a first exposure portion and a second exposure portion adjacent to each other on an exposure region of the photosensitive resin film with one time irradiation by an exposing apparatus; a step for performing heat treatment on the photosensitive resin film by a heating apparatus to measure the film thickness of the photosensitive resin film at the first and second exposure portions in the exposure region and the unexposed domain adjacent to the exposure region, thereby measuring a film thickness difference xcex94Tr1 between the first exposure portion and the unexposed domain and a film thickness difference xcex94Tr2 between the second exposure portion and the unexposed domain; a step for obtaining heating temperature during the heat treatment and actual irradiation amounts which have been irradiated on the first and second exposure portions from the film thickness differences xcex94Tr1 and xcex94Tr2 in the measured exposure region and a relationship between change in film thickness difference to change in exposing amount which has been obtained in advance and change in film thickness difference to change to the heating treating temperature; and a step for adjusting the heating apparatus/exposing apparatus from the obtained heating temperature and exposing amount, wherein the method comprises a step for forming a resist film on a substrate to be treated; a step for transferring a pattern formed on the exposure projection substrate onto the resist film; a step for performing heat treatment on the resist film by the heating apparatus; and a step for applying developing liquid to the resist film to selectively remove a portion of the resist film.
Furthermore, according to an eighth aspect of the present invention, there is provided a pattern forming method comprising a step for forming a resist film on a substrate to be treated; a step for performing exposure on the resist film by an exposing apparatus to transfer a pattern formed on a projection substrate onto the resist film; a step for performing heat treatment on the resist film by a heating apparatus; and a step for applying developing liquid to the resist film to selectively remove a portion of the resist film, wherein the transferring step comprises applying irradiation amounts Dopt1 and Dopt2 different from each other to a first exposure portion and a second exposure portion adjacent to each other on a monitor region of the resist film, and the heat treatment step comprises measuring the film thickness of the resist film at the first and second exposure portions and an unexposed domain adjacent thereto on the monitor region to measure a film thickness difference xcex94Tr1 between the first exposure portion and the unexposed domain on the monitor region and a film thickness difference xcex94Tr2 between the second exposure portion and the unexposed domain; obtaining heating temperature on the monitor region from the film thickness differences xcex94Tr1 and xcex94Tr2 on the measured monitor region and a relationship between change in film thickness difference to change in exposing amount which has been obtained in advance and change in film thickness difference to change in treating temperature; and heating the resist film while the control conditions of the heating apparatus is being adjusted in response to the obtained heating temperature.
Uniformity in dimension of intra-substrate and inter-substrate to be treated has been required according to making treating size fine. In a resist whose dimensions change largely according to heating temperature applied to the resist, evenness of the temperature applied to intra-substrate and inter-substrate to be treated has been required specifically.
In the present invention, an heating amount applied to a substrate to be treated is monitored by optically capturing information of a resist itself on the substrate to be treated during heating, namely change in film thickness or change in latent image. Further, the monitoring is performed using visible light or ultraviolet light having a shorter wavelength than infrared light. By reflecting this results on the heating means, it becomes possible to improve the evenness of the heating amount of the intra-substrate to be treated and the evenness of the heating amount of the inter-substrate to be treated, so that the uniformity in dimensions on the intra-substrate and the inter-substrate can be improved largely.
Accordingly, according to the present invention, the heating amount applied to a substrate to be treated can be controlled to be constant, and variations in dimensions of a resist pattern can be reduced, so that the present invention can contribute to improvement in reliability and production yield of the apparatuses.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.